The present invention relates, in general, to the field of computer systems and techniques for interconnecting various processing or computing elements. More particularly, the present invention relates to a hybrid computer system architecture and memory controller for close-coupling within a hybrid computing system using an adaptive processor interface port.
Hybrid computer systems are those that incorporate both standard microprocessors and adaptive processors. These are typically large multiprocessor server-type systems that reside on a shared network and are not directly operated with a user interface console. The overall performance and flexibility of such systems is directly proportional to the level of coupling between the microprocessors and the adaptive processors. That is to say, if the two processor types are treated as peers and have equal bandwidths and latencies to a shared memory, the system performance will be maximized.
To date, there have been several accepted methodologies for coupling the two forms of processors. The most basic of which was to connect the adaptive processor via the standard input/output (“I/O”) ports to the microprocessor. This is relatively simple in practice but provides only a very loose coupling with low bandwidths and high latencies relative to the bandwidths and latencies of the processor bus. Since both types of processors must share the same memory, this leads to significantly reduced performance in the adaptive processors. This technique also limits the amount of processor interaction that can realistically occur.
The second typical method of interconnection is to place the adaptive processor in the memory space of the microprocessor such as disclosed in certain specific embodiments disclosed in the aforementioned patents and patent applications. This connection yields a much tighter coupling as well as bandwidths and latencies typically equal to the microprocessor bus. However, particularly for small transfers, there may be more overhead associated with this connection than is desired. This is due to the “slaved” nature of the standard memory subsystem in a personal computer environment.
The third known method is to place the adaptive processor directly on the microprocessor bus or primary microprocessor interconnect (e.g. the Front Side Bus “FSB”). This method would seem to insure that the adaptive processor will have the same bandwidth and latency to the rest of the system as the microprocessors. However, in reality, this may not be true. In the case of Intel® microprocessors, a foreign device such as the adaptive processor, may be subject to special treatment and is classified as a third party agent. As such, it may not be able to use many features of the bus such as those associated with movement of cached data or data movement to I/O devices. It may also be the case that the adaptive processor is itself a whole circuit board and connection of it to the microprocessor may violate the bus layout ground rules. In addition, the adaptive processor would also have to participate in all of the microprocessor bus protocol, such as correctly responding to cache coherency related transactions, even though it may not be a coherent bus agent.